A study was conducted with the primary objective of examining the efficacy of delamination test using cylindrical core specimens to assess the bond quality of cross laminated timber (CLT) products. A prototype coring drill bit was fabricated to prepare a cylindrical-shaped specimen, the height of which corresponds to the full thickness of the CLT panel. A secondary objective was to examine the effect of pressure, adhesive type, number of plies, and specimen shape on the delamination resistance of CLT panels. The wood material used for the CLT samples was Select grade nominal 1 x 6-inch Hem-Fir boards. Examples of three adhesive types were evaluated, which were designated as A, B, and C. The delamination tests used were as described in CAN / CSA O122-06 and EN 302-2.
Cylindrical specimen extracted as core was found satisfactory as a test specimen type for use in delamination testing of CLT product. Its efficacy was comparable to that of a square cross-section specimen. The former is recommended as it can be extracted from thicker panels and from any location in the panel. It would also be more convenient to plug the round hole.
Adhesive type had a strong effect on delamination resistance based on the two delamination tests used. Adhesive A exhibited the greatest delamination resistance, followed in decreasing order, by adhesives C and B. It should be noted that no effort was made to find the optimum CLT manufacturing parameters for each type of adhesive. Therefore the relative rankings of the adhesives tested may not be representative. However, for the purposes of this study, the different performance levels from the three adhesives are useful in providing insight into how the proposed delamination test responds to significant changes in CLT manufacturing parameters.
Pressure used in fabricating the CLT panel showed a strong effect on delamination resistance as demonstrated for one of the adhesives. Delamination resistance decreased with decreasing pressure. The effect of the number of plies in the CLT panel was dependent upon the type of adhesive, and this was probably related to the adhesive’s assembly time characteristic. These results provide support as to the effectiveness of delamination test in assessing the moisture durability of CLT panels. It was able to differentiate the performance in delamination resistance among different types of adhesives, and able to detect the effect of manufacturing parameters such as pressure and increased number of plies in CLT construction.
The test procedure described in CAN / CSA O122-06 appears to be reasonable in the delamination resistance assessment of CLT panels for qualification and quality control testing. Based on the results of the study along with some background information and guidelines, delamination requirements for CLT panels are proposed. The permitted delamination values are greater than those currently specified for laminated and fingerjoined lumber products. This is in recognition of the higher bond line stresses when bonded perpendicular laminations (i.e. CLT) are exposed to the delamination wetting and drying cycles, as opposed to parallel laminations (i.e. glulam or fingerjoints).
A new design Section on Lateral Load Resisting Systems (LLRSs) was introduced in the 2009 edition of Canadian Standard for engineering Design in Wood (CSAO86). The activities presented in this report (development of technical papers, development of technical polls and attending various code committees) have a goal to continue the work in this field by further improving the new Section on LLRSs by implementing additional design information for other wood-based structural systems and assemblies. During the last two years several technical polls and papers were developed and presented to various code committees for future code implementation. These activities will help design engineers to use timber in structural systems in residential and non-residential buildings in Canada and the US.
This study was designed to evaluate the performance of a new wood-based portal frame system developed originally by APA with the purpose of providing alternative bracing systems to conventional prescribed details of small wood buildings. To achieve this objective, the study was divided into three components:
Study the performance of full-size portal frames with different configurations;
Evaluation of portal frame corners to optimize corner details and finally,
Develop a numerical model for portal frames to evaluate effect of the various parameters on performance and predict portal frame performance. Supplementary connections and material tests were conducted to generate input data for the finite element modelling of the portal frame.
Results from this preliminary test indicate that the lateral load carrying capacity of portal frames is approximately 75% the capacities of identical frames with hold-down. Those assemblies also had greater ultimate displacements than assemblies without hold-downs. Compared to portal frames without metal straps, the lateral load carrying capacity is slightly increased for with metal straps installed over sheathing. Same finding was observed in portal frame corner assembly tests. Full size portal frame and corner assemblies sheathed on one side without hold down had the lowest capacity among all assemblies tested. The addition of OSB sheathing to both sides of the portal frame corner has increased the moment resistance and rotational stiffness of the corner frame assembly.
Key findings from the FE modelling of portal frames with different types and locations of metal straps showed that the tensile strength of metal straps has the highest impact on the lateral load capacities and stiffness of portal frames assemblies. Portal frames assemblies with sheathings attached on both sides of the framing have approximately 30% higher lateral load capacities and stiffness than the walls with sheathings attached on one side of the framing. Moreover, it was found that it is more efficient to place metal straps directly on framing members. The efficiency is reduced if the metal straps are placed over the sheathing. The contribution of double bottom plates is insignificant. For portal frame assemblies with double bottom plates and two rows of nails fastened to the bottom plate, the stiffness and lateral load capacities are slightly increased compared to the walls with single bottom plate.